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Sunday, November 27, 2016

1[abc]a, b, or c (simple class)
2[^abc]Any character except a, b, or c (negation)
3[a-zA-Z]a through z or A through Z, inclusive (range)
4[a-d[m-p]]a through d, or m through p: [a-dm-p] (union)
5[a-z&&[def]]d, e, or f (intersection)
6[a-z&&[^bc]]a through z, except for b and c: [ad-z] (subtraction)
7[a-z&&[^m-p]]a through z, and not m through p: [a-lq-z](subtraction)

X? X, once or not at all
X* X, zero or more times
X+ X, one or more times
X{n} X, exactly n times
X{n,} X, at least n times
X{n,m} X, at least n but not more than m times

Reluctant quantifiers
X?? X, once or not at all
X*? X, zero or more times
X+? X, one or more times
X{n}? X, exactly n times
X{n,}? X, at least n times
X{n,m}? X, at least n but not more than m times

Possessive quantifiers
X?+ X, once or not at all
X*+ X, zero or more times
X++ X, one or more times
X{n}+ X, exactly n times
X{n,}+ X, at least n times
X{n,m}+ X, at least n but not more than m times